This invention relates to a method and apparatus for identifying tissue, which may be human or animal tissue.
The infrared spectra of the malignant tissue and the normal mucosa of the human colon have been measured. For example, U.S. Pat. No. 5,038,039 described a method of detecting the presence of anomalies in biological tissues and cells in natural and cultured form (e.g. cancerous tissues or cells) is detected by infrared spectroscopy. A beam of infrared light is directed at a sample of tissues or cells in natural or cultured form containing the cells to be tested, and the anomaly is detected at at least one range of frequencies by determining whether changes in infrared absorption have occurred due to the vibration of at least one functional group of molecules present in the sample which is characteristic of the anomaly.
U.S. Pat. No. 5,168,162 describes a method of detecting the presence of anomalies in exfoliated cells using infrared spectroscopy wherein the anomaly is detected in at least one range of frequencies by determining whether changes in infrared absorption has occurred which is due to functional group vibration in, for example, phosphodiester groups of nucleic acids, COH groups of tissue proteins, carbohydrates, or due to special arrangements of lipid molecules or abnormal lipid structures, present in the specimen.
While this approach, i.e. interpreting the changes in the spectra from normal mucosa to malignant tissue in terms of structural changes at the molecular level, is of considerable value, a problem can arise due to the fact that colonic mucosa is composed of glandular epithelium and lamina propria which is mainly loose connective tissue. Malignant tumors of the colon are derived almost exclusively from the epithelium. Therefore, the changes in the spectra may entirely arise from the differences between the connective tissue and the epithelial tissue of the colon and may not be the consequence of the structural changes of the tissue molecules in the pathway of carcinogenesis. Moreover, the spectra of the colon mucosa are very similar to the spectrum of the cervical connective tissue, which indicates that the colonic mucosa samples may be mainly connective tissue and may not contain any epithelium.